EASY (IER) KANJI - JLPT 3 KYUU

Think of a karate expert jumping in the air to break a board in two
  1) kuu, 2) kara, 3) sora - sky, air, empty
空手 kara te - karate [lit. empty hand]
空気 kuu ki - air, atmosphere
空港 kuu kou - airport
sora - sky